The principal components of bauxite are aluminium and iron compounds. In the production of alumina from bauxites, the maximum possible fraction of aluminium oxide is recovered, whereas all iron compounds are stockpiled; up to a million tons per year of iron oxide can accumulate in some alumina production units. The separation of the iron compounds in the production of alumina leads not only to an improvement in the process parameters of the working steps for concentrating and washing red mud or for sintering the mud batch, but also has a positive environmental influence by extending the lifetime of mud fields.
Processes are known for separating iron both from bauxite and from red mud. In the Pedersen Process, a mixture of bauxite and calcium oxide is melted in an electric arc furnace at a temperature of 1500° C. to produce pig iron and aluminium-calcium slag that is further processed hydrometallurgically to produce alumina (see Ni L. P., Goldman M. M., Solenko T. V. Pererabotka vysoko{hacek over (z)}elezistych boksitov—Metallurgija, M., 1979, S. 203).
The modified sequential variant of the Bayer Process is also known. The process involves sintering with an intermediate step of iron separation by melting red mud in the presence of a reducing agent at a temperature of 1250-1300° C. according to the Krupp-Renn Process with magnetic separation of iron, sintering the slag with limestone and soda at 1200° C., leaching the sinter cake in order to obtain a sodium aluminate solution and using the mud to produce cement (ibid., p 205).
The process of magnetizing calcination of siderite-containing bauxite is known for the purpose of siderite decomposition and the conversion of the iron compounds into magnetic compounds with their subsequent recovery by means of magnetic separation (ibid., p 215).
The above processes for the separation of iron from both bauxite and red mud require pyrometallurgical steps of calcination and melting, thereby necessitating an increase in constructional capital costs and in running costs for energy sources and the reducing agent. The pyrometallurgical process steps are linked with considerable environmentally harmful emissions.
One solution is a process for the extraction of aluminium and iron from aluminium-containing ores (see U.S. Pat. No. 2,155,919). Processes for the extraction of aluminium and iron ions from aluminum-containing ores are described in this patent document. The ore extraction process includes leaching roasted ore with the use of acid to produce a leachate and a solid precipitate. The leachate has aluminium and iron ions in solution. The process for recovering the aluminium ions from a mixture that comprises the Iron and aluminium ions involves recovery of the aluminium ions, an organic solvent and an extractant that is capable of producing an organometallic complex essentially selectively with the iron or aluminium ions, which are soluble in the organic solvent.
The disadvantage of this process is in the need for the ore roasting and in the difficulty of recovering the acid in the course of the leaching, all of which requiring an increased energy output and being very environmentally harmful.